In blockchain, when a transaction is first equested, it is authenticated using cryptographic keys (public and private keys). Then a block containing that transaction is created and sent to the entire network. Once the transaction is agreed between the nodes in the network, it is approved (i.e., authorised) before the block is added to the chain. This is done by a mechanism called consensus, where the majority of nodes agree with the transaction. Note that nodes must perform a complex mathematical problem to validate a transaction. This is known as mining, and the participanting nodes are referred to as the miners. Commonly, the mining task in called Proof of Work (PoW). A cryptocurrency reward is given to the miner who first solves the mathematical problem (i.e., the PoW) and validates a block. After this, the block is added to the existing chain, and all the nodes in the network are updated with this information [1]}.
